I'm in the same boat - I too have my one and only interview next week. I always felt it was unlikely that faculty would actually ask about what other schools you've heard from and things like that, but maybe I'm wrong. If asked, I'd plan to be honest and say that I haven't heard back from most other schools yet. However, the question of how likely you'd be to take an offer at that school might be a good opportunity for you to discuss your fit with the program, rather than commit yourself to the program on the spot.